Image sensor and image capturing apparatus

ABSTRACT

An image capturing apparatus in which a plurality of pixels each having a plurality of photoelectric conversion units for receiving light fluxes that have passed through different partial pupil regions of an imaging optical system are arrayed, wherein an entrance pupil distance Z s  of the image sensor with respect to a minimum exit pupil distance L min  of the imaging optical system and the maximum exit pupil distance L max  of the imaging optical system satisfies a condition of 
     
       
         
           
             
               
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BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an image sensor and an image capturingapparatus.

Description of the Related Art

As a focus detection method performed by an image capturing apparatus,an on-imaging surface phase difference method is used in which focusdetection by a phase difference method is performed using focusdetection pixels formed in an image sensor.

U.S. Pat. No. 4,410,804 discloses an image capturing apparatus using atwo-dimensional image sensor in which one microlens and a plurality ofphotoelectric conversion units are formed in each pixel. The pluralityof photoelectric conversion units are configured to receive lightcomponents that have passed through different regions of the exit pupilof an imaging lens via one microlens, thereby dividing the pupil. Acorrelation amount is calculated from focus detection signals outputfrom pixels (focus detection pixels) each including a plurality ofphotoelectric conversion units, and an image shift amount is obtainedfrom the correlation amount, thereby performing focus detection by thephase difference method. Further, Japanese Patent Laid-Open No.2001-083407 discloses generating an image signal by adding focusdetection signals output from a plurality of photoelectric conversionunits for each pixel.

Japanese Patent Laid-Open No. 2000-156823 discloses an image capturingapparatus in which pairs of focus detection pixels are partiallyarranged in a two-dimensional image sensor formed from a plurality ofimaging pixels. The pairs of focus detection pixels are configured toreceive light components from different regions of the exit pupil of animaging lens via a light shielding layer having openings, therebydividing the pupil. An image signal is acquired by imaging pixelsarranged on most part of the two-dimensional image sensor. A correlationamount is calculated from focus detection signals of the partiallyarranged focus detection pixels, and an image shift amount is obtainedfrom the calculated correlation amount, thereby performing focusdetection by the phase difference method, as disclosed.

In focus detection using the on-imaging surface phase difference method,the defocus direction and the defocus amount can simultaneously bedetected by focus detection pixels formed in an image sensor. It istherefore possible to perform focus control at a high speed.

However, in the on-imaging surface phase difference method, there is aproblem in that, when a variation range of an incident angle of lightfrom an imaging lens (imaging optical system) on an image sensor at aperipheral portion is large, a pupil deviation between an entrance pupilof a sensor and an exit pupil of the imaging lens is large, and the baseline length is not secured, and consequently there is a case in whichthe focus detection quality by the on-imaging surface phase differencemethod deteriorates.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the abovesituation, and realizes focus detection by the on-imaging surface phasedifference method under a wide range of conditions in a case where avariation range of an incident angle of light from an imaging opticalsystem on an image sensor at a peripheral portion is large.

According to the present invention, provided is an image capturingapparatus in which a plurality of pixels each having a plurality ofphotoelectric conversion units for receiving light fluxes that havepassed through different partial pupil regions of an imaging opticalsystem are arrayed, wherein an entrance pupil distance Z_(s) of theimage sensor with respect to a minimum exit pupil distance L_(min) ofthe imaging optical system and the maximum exit pupil distance L_(max)of the imaging optical system satisfies a condition of

$\frac{4L_{\min}L_{\max}}{L_{\min} + {3L_{\max}}} < Z_{S} < {\frac{4L_{\min}L_{\max}}{{3L_{\min}} + L_{\max}}.}$

Further, according to the present invention, provided is an image sensorin which a plurality of pixels each having a plurality of photoelectricconversion units for receiving light fluxes that have passed throughdifferent partial pupil regions of an imaging optical system arearrayed, wherein an entrance pupil distance Z_(s) of the image sensorwith respect to a maximum image height R of the image sensor satisfiesthe condition of 2.33R<Z_(s)<6.99R.

Furthermore, according to the present invention, provided is an imagesensor in which a plurality of pixels each having a plurality ofphotoelectric conversion units for receiving light fluxes that havepassed through different partial pupil regions of an imaging opticalsystem are arrayed, wherein a maximum image height and an entrance pupildistance of the image sensor is determined such that a deviation amountbetween the entrance pupil of the image sensor and an exit pupil of theimaging optical system with respect to each of the plurality ofphotoelectric conversion units falls within a predetermined range.

Further, according to the present invention, provided is an imagecapturing apparatus that is capable of connecting to an exchangeableimaging optical system comprising the image sensor as described above.

Further, according to the present invention, provided is an imagecapturing apparatus comprising: the imaging optical system; and theimage sensor as described above.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the description, serve to explain the principles of theinvention.

FIG. 1 is a schematic block diagram of an image capturing apparatusaccording to an embodiment of the present invention;

FIG. 2 is a schematic view of a pixel array according to the embodiment;

FIGS. 3A and 3B are a schematic plan view and a schematic sectionalview, respectively, of a pixel according to the embodiment;

FIG. 4 is a schematic explanatory view of a pixel structure and pupildivision according to the embodiment;

FIG. 5 is a schematic explanatory view of an image sensor and pupildivision according to the embodiment;

FIG. 6 is a schematic explanatory view for explaining correspondencebetween an entrance pupil of an image sensor and a pupil shift amountbetween the entrance pupil and an exit pupil of an imaging opticalsystem according to the embodiment;

FIG. 7 is a schematic view of a pixel array according to a modification;

FIGS. 8A and 8B are a schematic plan view and a schematic sectionalview, respectively, of a pixel according to the modification;

FIGS. 9A and 9B are diagrams showing an example of light intensitydistribution within a pixel according to the embodiment; and

FIG. 10 is a diagram showing an example of pupil intensity distributionaccording to the embodiment.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will be described indetail in accordance with the accompanying drawings.

[Overall Arrangement]

FIG. 1 is a diagram showing a brief configuration of a camera as anexample of an image capturing apparatus having an image sensor accordingto an embodiment of the present invention. In FIG. 1, a first lens group101 is disposed on the front end of an imaging optical system, andsupported so as to be movable forward and backward along an opticalaxis. An aperture-shutter 102 adjusts the diameter of its opening,thereby adjusting the amount of light during image sensing, and also hasa function to adjust the exposure time during still image sensing. Theaperture-shutter 102 and a second lens group 103 move together forwardand backward along the optical axis, and, in conjunction with themovement forward and backward of the first lens group 101, provide amagnification change effect (a zoom function).

A third lens group 105 (focus lens) carries out focus adjustment bymoving forward and backward along the optical axis. A low-pass opticalfilter 106 is an optical element for the purpose of reducing false colorand moire of a sensed image. An image sensor 107 is composed of atwo-dimensional CMOS photo sensor and the surrounding circuitry, anddisposed on an imaging plane of the imaging optical system.

A zoom actuator 111 carries out a magnification-change operation byrotation of a cam barrel, not shown, to move the first lens group 101through the second lens group 103 forward and backward along the opticalaxis. An aperture-shutter actuator 112 controls the diameter of theopening of the aperture-shutter 102 and adjusts the amount of light forimage sensing, and also controls the exposure time during still imagesensing. A focus actuator 114 moves the third lens group 105 forward andbackward along the optical axis to adjust the focus.

An electronic flash 115 for illuminating an object is used during imagesensing. A flash illumination device that uses a Xenon tube ispreferable, but an illumination device comprised of a continuous-flashLED may also be used. An AF auxiliary flash unit 116 projects an imageof a mask having a predetermined opening pattern onto an object fieldthrough a projective lens to improve focus detection capability withrespect to dark objects and low-contrast objects.

The CPU 121 controls the camera main unit in various ways within theimage capturing apparatus. The CPU 121 may, for example, have acalculation unit, ROM, RAM, A/D converter, D/A converter, communicationinterface circuitry, and so forth. In addition, the CPU 121, based onpredetermined programs stored in the ROM, drives the various circuitsthat the camera has, and executes a set of operations of AF, imagesensing, image processing, and recording.

An electronic flash control circuit 122 controls firing of theelectronic flash 115 in synchrony with an image sensing operation. Anauxiliary flash drive circuit 123 controls firing of the AF auxiliaryflash unit 116 in synchrony with a focus detection operation. An imagesensor drive circuit 124 controls the image sensing operation of theimage sensor 107 as well as A/D-converts acquired image signals andtransmits the converted image signals to the CPU 121. An imageprocessing circuit 125 performs such processing as γ conversion, colorinterpolation, JPEG compression and the like on the images acquired bythe image sensor 107.

A focus drive circuit 126 controls the drive of the focus actuator 114based on the focus detection result to drive the third lens group 105reciprocally in the optical axis direction, thereby performing focusadjustment. An aperture-shutter drive circuit 128 controls the drive ofthe aperture-shutter actuator 112, thereby driving the opening of theaperture-shutter 102. A zoom drive circuit 129 drives the zoom actuator111 in accordance with the zoom operation of the user.

A display device 131, such as an LCD, displays information relating tothe image sensing mode of the camera, preview images before imagesensing, confirmation images after image sensing, focus state displayimages during focus detection, and the like. An operating switch group132 is composed of a power switch, a release (image sensing trigger)switch, a zoom operation switch, an image sensing mode selection switch,and the like. A detachable flash memory 133 records captured images.

[Image Sensor]

FIG. 2 shows the outline of an array of the imaging pixels and the focusdetection pixels of the image sensor 107 according to the embodiment.FIG. 2 illustrates the pixel (imaging pixel) array within the range of 4columns×4 rows and the focus detection pixel array within the range of 8columns×4 rows in the two-dimensional CMOS sensor (image sensor)according to this embodiment.

A pixel group 200 includes pixels of 2 columns×2 rows. A pixel 200Rhaving an R (red) spectral sensitivity is arranged at the upper leftposition, pixels 200G having a G (green) spectral sensitivity arearranged at the upper right and lower left positions, and a pixel 200Bhaving a B (blue) spectral sensitivity is arranged at the lower rightposition. Each pixel is formed from a first focus detection pixel 201and a second focus detection pixel 202 arrayed in 2 columns×1 row.

A number of arrays of 4 (columns)×4 (rows) pixels (8 (columns)×4 (rows)focus detection pixels) shown in FIG. 2 are arranged on a plane toenable to capture an image (focus detection signal). In the embodiment,the image sensor will be described assuming that the horizontal size His 36 mm, and the vertical size V is 24 mm, a period P of pixels is 4.8μm, the number N of pixels is 7,500 columns in horizontal direction x5,000 rows in vertical direction=37,500,000, a column-direction periodPAF of focus detection pixels is 2.4 μm, and the number NAF of focusdetection pixels is 15,000 columns in horizontal direction×5,000 rows invertical direction=75,000,000.

FIG. 3A is a plan view of one pixel 200G of the image sensor 107 shownin FIG. 2 when viewed from the light receiving surface side (+z side) ofthe image sensor 107, and FIG. 3B is a sectional view showing the a-asection in FIG. 3A viewed from the −y side. As shown in FIGS. 3A and 3B,in the pixel 200G according to this embodiment, a microlens 305 forcondensing incident light is formed on the light receiving side of eachpixel. The pixel is divided by NH (here, divided by two) in the xdirection and divided by NV (here, divided by one, or not divided) inthe y direction to form photoelectric conversion units 301 and 302. Thephotoelectric conversion units 301 and 302 correspond to the first focusdetection pixel 201 and the second focus detection pixel 202,respectively.

Each of the photoelectric conversion units 301 and 302 may be formed asa pin structure photodiode including an intrinsic layer between a p-typelayer and an n-type layer or a p-n junction photodiode without anintrinsic layer, as needed.

In each pixel, a color filter 306 is formed between the microlens 305and the photoelectric conversion units 301 and 302. The spectraltransmittance of the color filter may be changed between the focusdetection pixels, as needed, or the color filter may be omitted.

Light that has entered the pixel 200G shown in FIGS. 3A and 3B iscondensed by the microlens 305, spectrally split by the color filter306, and received by the photoelectric conversion units 301 and 302. Inthe photoelectric conversion units 301 and 302, electron-hole pairs areproduced in accordance with the received light amount and separated inthe depletion layer. Electrons having negative charges are accumulatedin the n-type layers (not shown). On the other hand, holes aredischarged externally from the image sensor 107 through the p-typelayers connected to a constant voltage source (not shown). The electronsaccumulated in the n-type layers (not shown) of the photoelectricconversion units 301 and 302 are transferred to electrostaticcapacitances (FDs) through transfer gates, converted into voltagesignals, and output. Note that the focus position of the microlens 305changes in accordance with its shape (curvature, for example), material(index of refraction, for example), and positional relationship withrespect to corresponding photoelectric conversion units, and so on. Bysetting these parameters, it is possible to set the focus position ofthe microlens 305.

The pixels 200R and 200B shown in FIG. 2 also have the similar structureas the pixel 200G, and output voltage signals corresponding to the lightspectrally split by the color filter 306, in a similar manner as thepixel 200G.

The correspondence between pupil division and the pixel structureaccording to this embodiment shown in FIGS. 3A and 3B will be describedwith reference to FIG. 4. FIG. 4 illustrates a sectional view showingthe a-a section of the pixel structure according to the embodiment shownin FIG. 3A viewed from the +y side and the exit pupil plane of animaging optical system. Note that in FIG. 4, to obtain correspondencewith the coordinate axes of the exit pupil plane, the x- and y-axes ofthe sectional view are reversed with respect to those of FIGS. 3A and3B.

A first partial pupil region 501 of the first focus detection pixel 201represents a pupil region that is almost conjugate with the lightreceiving surface of the photoelectric conversion unit 301 having acenter of gravity decentered in the −x direction via the microlens 305,and light beams that have passed through the first partial pupil region501 are received by the first focus detection pixel 201. The firstpartial pupil region 501 of the first focus detection pixel 201 has acenter of gravity decentered to the +x side on the pupil plane.

A second partial pupil region 502 of the second focus detection pixel202 represents a pupil region that is almost conjugate with the lightreceiving surface of the photoelectric conversion unit 302 having acenter of gravity decentered in the +x direction via the microlens 305,and light beams that have passed through the second partial pupil region502 are received by the second focus detection pixel 202. The secondpartial pupil region 502 of the second focus detection pixel 202 has acenter of gravity decentered to the −x side on the pupil plane.

Light beams that have passed through a pupil region 500 are received bythe whole pixel 200G including the photoelectric conversion units 301and 302 (first focus detection pixel 201 and the second focus detectionpixel 202). Reference numeral 400 denotes an opening of theaperture-shutter 102.

FIG. 5 is a schematic view showing the correspondence between the imagesensor and pupil division according to the embodiment. It is configuredso that, at a sensor entrance pupil distance Z_(s), the first partialpupil region 501 corresponding to a light receiving region of the firstfocus detection pixel 201 of each pixel arranged at each position on thesurface of the image sensor 107 substantially matches. Similarly, it isconfigured so that the second partial pupil region 502 corresponding toa light receiving region of the second focus detection pixel 202 of eachpixel substantially matches. In other words, it is configured so that apupil division position between the first partial pupil region 501 andthe second partial pupil region 502 for each pixel of the image sensor107 substantially matches at the sensor entrance pupil distance Z_(s).The first partial pupil region 501 and the second partial pupil region502 are referred to as “sensor entrance pupil”, hereinafter. A pair oflight fluxes that have passed through the different partial pupilregions of an imaging optical system, namely, the first partial pupilregion 501 and the second partial pupil region 502 are incident on eachpixel of the image sensor 107 at different incident angles, and receivedby the first focus detection pixel 201 and the second focus detectionpixel 202 which are divided to 2×1. The present embodiment shows a casewhere the pupil region is divided into two in the horizontal direction.However, the pupil region may be divided in the vertical direction asneeded.

FIGS. 9A and 9B show light intensity distributions in a case where lightis incident on a microlens formed in each pixel. FIG. 9A shows a lightintensity distribution of a cross section of the microlens that isparallel to the optical axis of the microlens. FIG. 9B shows a lightintensity distribution of a cross section of the microlens that isperpendicular to the optical axis of the microlens at a focus positionof the microlens. Incident light is converged by the microlens to thefocus position. However, due to diffraction caused by the fluctuation oflight, it is not possible to make the diameter of a concentration spotof light smaller than the diffraction limit Δ, and must have a finitesize. The size of the light receiving surface of a photoelectricconversion unit is about 1 to 2 μm, whereas the size of theconcentration spot of the microlens is about 1 μm. Therefore, the firstpartial pupil region 501 and the second partial pupil region 502 in FIG.4 which are conjugate with the light receiving surface of thephotoelectric conversion unit with respect to the microlens are notpupil divided precisely due to diffraction blur, and receive light inaccordance with light receiving rate distribution (pupil intensitydistribution) that depends on an incident angle of light.

FIG. 10 shows an example of the light receiving rate distribution (pupilintensity distribution) that depends on an incident angle of light. Theabscissa indicates an incident angle of light θ (can be converted topupil coordinates), and the ordinate indicates a light receiving rate. Acurve PI1 (θ) shown by a broken line in FIG. 10 illustrates a pupilintensity distribution of the first partial pupil region 501 in FIG. 4along the X axis, and a curve PI2 (θ) shown by a dot-dash lineillustrates a pupil intensity distribution of the second partial pupilregion along the X axis. Further, a curve PI(θ) (=PI1 (θ)+PI2 (θ)) shownby a solid line illustrates a pupil intensity distribution of the totalpupil region 500 of the first partial pupil region 501 and the secondpartial pupil region 502 in FIG. 4 along the X axis. As shown in FIG.10, it will be understood that the pupil is divided gradually.

The embodiment shows an example in which the pupil region is dividedinto two in the horizontal direction. However, the pupil region may bedivided in the vertical direction as needed.

It should be noted that, in the aforesaid example, a plurality of imagesensing pixels each formed with the first focus detection pixel and thesecond focus detection pixel are arrayed, however, the present inventionis not limited to this. The image sensing pixels, the first focusdetection pixels and the second focus detection pixels may be formedindependently, and the first focus detection pixels and the second focusdetection pixels may be partially provided among an array of the imagesensing pixels.

In this embodiment, the first focus detection signal is formed bycollecting signals corresponding to received light from the first focusdetection pixels 201 of the respective pixels of the image sensor, thesecond focus detection signal is formed by collecting signalscorresponding to received light from the second focus detection pixels202 of the respective pixels of the image sensor, and perform focusdetection using the first and second focus detection signals. Further,by adding the signals from the first focus detection pixels 201 and thesecond focus detection pixels 202 for each pixel of the image sensor107, an image signal (a captured image) with the resolutioncorresponding to the number of the effective pixels N is generated.

[Pupil Deviation]

FIG. 6 is a schematic explanatory view of corresponding relationship ofa pupil deviation between the entrance pupil of the image sensor 107 ofthis embodiment (referred to as “sensor entrance pupil”, hereinafter)and the exit pupil of the imaging optical system (referred to as“imaging lens exit pupil”, hereinafter). In FIG. 6, let the entrancepupil distance of the image sensor 107 (referred to as “sensor entrancepupil distance”, hereinafter) be Z_(s), the maximum image height of theimage sensor 107 be R, the minimum exit pupil distance of the imagingoptical system be L_(min), and the maximum exit pupil distance of theimaging optical system be L_(max). The maximum image height R of theimage sensor 107 is R²=(0.5×H)²+(0.5×V)², with the horizontal size ofthe image sensor 107 being H, and the vertical size of the image sensor107 being V. The exit pupil distance of the imaging optical systemchanges between the minimum exit pupil distance L_(min) and the maximumexit pupil distance L_(max) in accordance with the exchange of theimaging lens in a case of lens exchangeable camera, changes in a zoomratio, focus state, and aperture of the imaging lens. Further, in thisembodiment, the image height is an amount determined independent of theimage height of the imaging lens, and used as a position from the centerof the image sensor 107 or the position from the center of a sensedimage. Therefore, although calculation of the maximum image height R hasbeen explained using the horizontal size H and the vertical size V,these sizes do not necessarily coincide with the size of the imagesensor 107. For example, the maximum image height R may be the maximumimage height of an image to be displayed on the display device 131, inwhich case, the maximum image height R may be smaller than the size ofthe image sensor 107 by an amount of a margin used for image processingand image stabilization. Further, the maximum image height R may be themaximum image height of an image portion to be stored as image data. Inthis case, the image portion substantially coincides with an area inwhich calculation for the focus detection is performed.

At the sensor entrance pupil distance Z_(s), the first partial pupilregion 501 which is a light receiving region (entrance pupil) of thefirst focus detection pixel 201 of each pixel of the image sensor 107and the second partial pupil region 502 which is a light receivingregion of the second focus detection pixel 202 intersect substantiallyon the optical axis. Considering the overlapping of the first partialpupil region 501 and the second partial pupil region 502, which are thesensor entrance pupil, and the imaging lens exit pupil at the sensorentrance pupil distance Z_(s) , a pupil deviation amount between thesensor entrance pupil and the imaging lens exit pupil with the minimumexit pupil distance L_(min) is P1. Similarly, a pupil deviation amountbetween the sensor entrance pupil and the imaging lens exit pupil withthe maximum exit pupil distance L_(max) is P2. If either of the pupildeviation amount P1 or the pupil deviation amount P2 between the sensorentrance pupil and the imaging lens exit pupil is large, the base-linelength is not secured, and there is case in which the focus detectionperformance by the phase difference AF deteriorates.

Accordingly, in the present embodiment, it is configured such that thesensor entrance pupil distance Z_(s) satisfies the following conditionso that the pupil deviation amounts P1 and P2 are restrained.

First, let an incident angle of light on a pixel located at the maximumimage height R of the image sensor 107 from the sensor entrance pupildistance Z_(s) on the optical axis be θ_(s), an incident angle of lighton the same pixel from the minimum exit pupil distance L_(min) on theoptical axis be θ_(max), and an incident angle of light on the samepixel from the maximum exit pupil distance L_(max) on the optical axisbe θ_(min). In order to restrain the pupil deviation amounts P1 and P2to secure the base-line length, in this embodiment, the angle θ_(s) isset within a range that satisfies the following expression (1) whichdefines a neighboring range of an average incident angle.

$\begin{matrix}{\frac{\theta_{\max} + {3\; \theta_{\min}}}{4} < \theta_{S} < \frac{{3\; \theta_{\max}} + \theta_{\min}}{4}} & (1)\end{matrix}$

Further, θ_(s), θ_(max), and θ_(min) can be approximated by thefollowing expressions (2).

$\begin{matrix}{{{\theta_{S} \cong {\tan \; \theta_{S}}} = \frac{R}{Z_{S}}}{{\theta_{\max} \cong {\tan \; \theta_{\max}}} = \frac{R}{L_{\min}}}{{\theta_{\min} \cong {\tan \; \theta_{\min}}} = \frac{R}{L_{\max}}}} & (2)\end{matrix}$

By substituting the expression (2) to the expression (1), the followingexpression (3) that shows the condition that the sensor entrance pupildistance Z_(s) should satisfy is obtained.

$\begin{matrix}{\frac{4L_{\min}L_{\max}}{L_{\min} + {3L_{\max}}} < Z_{S} < \frac{4L_{\min}L_{\max}}{{3L_{\min}} + L_{\max}}} & (3)\end{matrix}$

Therefore, in this embodiment, in order to restrain the pupil deviationamounts P1 and P2 and secure the base-line length, it is configured sothat the entrance pupil distance Z_(s) of the image sensor 107 satisfiesthe expression (3) with the minimum exit pupil distance L_(min) and themaximum exit pupil distance L_(max) of the imaging optical system.

In a case of a lens exchangeable camera, lenses with various opticalconditions, from the wide angle lenses to telephoto lenses may beattached. In this case, as a condition for the maximum exit pupildistance L_(max) of the imaging optical system, it is desired to setL_(max)=∞ in order to cope with the telecentric optical lens. Further,as a condition for the minimum exit pupil distance L_(min) of theimaging optical system, it is desired to restrain a marginalillumination decrease expressed by the cosine fourth law with respect tothe center image height to equal to or less than ½ (half). Therefore,under the condition of cos⁴(θ_(max))=½, it is desired that the maximumincident angle θ_(max) of light that incidents on the pixel located atthe maximum image height R of the image sensor 107 from the minimum exitpupil distance L_(min) on the optical axis is θ_(max)=32.8°=0.572[rad].Accordingly, from the expression (2), with the maximum image height R ofthe image sensor 107, it is desired that minimum exit pupil distanceL_(min) is L_(min)=R/0.572.

By substituting L_(min)=R/0.572 and L_(max)=∞ in the expression (3), thefollowing condition expression (4) for the sensor entrance pupildistance Z_(s) is obtained.

2.33R<Z_(s)<6.99R   (4)

In this embodiment, since the horizontal size H of the image sensor 107is 36 mm, the vertical size V of the same is 24 mm, and the maximumimage height R of the same is 21.63 mm, the condition expression (4) forthe sensor entrance pupil distance Z_(s) is 50.4 mm<Z_(s)<151.2 mm.

Further, the condition of the minimum exit pupil distance L_(min) of theimaging optical system may be determined on the basis of the pupilintensity distribution of the pupil region 500 which is a combined areaof the first partial pupil region 501 and the second partial pupilregion 502 of the image sensor 107. Here, the pupil intensitydistribution of the pupil region 500 at the central image height isdenoted by PI0 (θ), and the pupil intensity distribution of the pupilregion 500 at the maximum image height R is denoted by PIR (θ). As thecondition of the minimum exit pupil distance L_(min) of the imagingoptical system, it is desirable to restrain a decrease in the pupilintensity distribution PIR(θ=θ_(max PIR)) at the incident angleθ_(max PIR)[rad] at the maximum image height R to ½ (half) or less thanthe pupil intensity distribution PI0 (θ=0) at the incident angle 0 [rad]at the central image height. Therefore, it is desirable to determine theincident angle θ_(max PIR) of light from the minimum exit pupil distanceL_(min) on the optical axis based on the condition of PIR(θ=θ_(max PIR))=0.5×PI0 (θ=0) , and determine the minimum exit pupildistance L_(min)=R/θ_(max PIR) from the expression (2).

By substituting L_(min)=R/θ_(max PIR) and L_(max)=∞ to the expression(3), the condition expression (5) of the sensor entrance pupil distanceZ_(s) is obtained.

$\begin{matrix}{{\frac{4}{3}\frac{R}{\theta_{max\_ PIR}}} < Z_{S} < {4\frac{R}{\theta_{max\_ PIR}}}} & (5)\end{matrix}$

As described above, the image sensor of the embodiment has aconfiguration in which a plurality of pixels are arrayed, wherein eachpixel has a plurality of photoelectric conversion units for receivinglight fluxes that have passed through different partial pupil regions ofthe imaging optical system, and in which the sensor entrance pupildistance Z_(s) satisfies the expression (3) with respect to the minimumexit pupil distance L_(min) of the imaging optical system and themaximum exit pupil distance L_(max) of the imaging optical system.

Further, the image sensor of the embodiment has a configuration in whicha plurality of pixels are arrayed, wherein each pixel has a plurality ofphotoelectric conversion units for receiving light fluxes that havepassed through different partial pupil regions of the imaging opticalsystem, and in which the sensor entrance pupil distance Z_(s) satisfiesthe expression (4) with respect to the maximum image height R of theimage sensor.

With the configuration as described above, the focus detection by theon-imaging surface phase difference method is possible over a wide rangeof conditions in a case where a changing range of the incident angle oflight from the imaging optical system on a pixel at a peripheral imageheight of the image sensor is large.

<Modification>

In the first embodiment as described above, each pixel of the imagesensor 107 is divided by 2 in the x direction, and by 1 (or not divided)in the y direction. However, the present invention is not limited tothis, an image sensor 107 comprises pixels that are divided by differentnumbers and different ways from the pixels shown in FIG. 2.

FIG. 7 shows the outline of the imaging pixels and the array of focusdetection pixels of the image sensor 107 according to the modification.FIG. 7 illustrates the pixel (imaging pixel) array within the range of 4columns×4 rows and the focus detection pixel array within the range of 8columns×8 rows in the two-dimensional CMOS sensor (image sensor)according to the modification.

In this modification, a pixel group 700 shown in FIG. 7 includes pixelsof 2 columns×2 rows. A pixel 700R having an R (red) spectral sensitivityis arranged at the upper left position, pixels 700G having a G (green)spectral sensitivity are arranged at the upper right and lower leftpositions, and a pixel 700B having a B (blue) spectral sensitivity isarranged at the lower right position. Each pixel is formed from a firstfocus detection pixel 701 to a fourth focus detection pixel 704 arrayedin 2 columns×2 rows.

A number of arrays of 4 (columns)×4 (rows) pixels (8 (columns)×8 (rows)focus detection pixels) shown in FIG. 7 are arranged on a plane toenable to capture an image (focus detection signal). In themodification, the image sensor will be described assuming that thehorizontal size H is 36 mm, vertical size V is 24 mm, a period P ofpixels is 4.8 μm, the number N of pixels is 7,500 columns in horizontaldirection×5,000 rows in vertical direction=37,500,000, acolumn-direction period PSUB of focus detection pixels is 2.4 μm, andthe number NSUB of focus detection pixels is 15,000 columns inhorizontal direction x 10,000 rows in vertical direction=150,000,000.

FIG. 8A is a plan view of one pixel 700G of the image sensor 107 shownin FIG. 7 when viewed from the light receiving surface side (+z side) ofthe image sensor 107, and FIG. 8B is a sectional view showing the a-asection in FIG. 8A viewed from the −y side. As shown in FIGS. 8A and 8B,in the pixel 700G according to the modification, a microlens 305 forcondensing incident light is formed on the light receiving side of eachpixel. The pixel is divided by NH (here, divided by two) in the xdirection and divided by NV (here, divided by two) in the y direction toform first to fourth photoelectric conversion units 801 to 804. Thefirst to fourth photoelectric conversion units 801 to 804 correspond tothe first focus detection pixel 701 to the fourth focus detection pixel704, respectively.

In the modification, by adding signals from the first focus detectionpixel 701 to the fourth focus detection pixel 704 for each pixel of theimage sensor 107, an image signal (a captured image) with the resolutioncorresponding to the number of the effective pixels N is generated.Except for this, the modification is similar to the above embodiment.

With the configuration as described above, the focus detection by theon-imaging surface phase difference method is possible over a wide rangeof conditions in a case where a changing range of the incident angle oflight from the imaging optical system on a pixel at a peripheral imageheight of the image sensor is large.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application Nos.2016-016173, filed on Jan. 29, 2016 and 2016-234423, filed on Dec. 1,2016, which are hereby incorporated by reference herein in theirentirety.

What is claimed is:
 1. An image capturing apparatus in which a pluralityof pixels each having a plurality of photoelectric conversion units forreceiving light fluxes that have passed through different partial pupilregions of an imaging optical system are arrayed, wherein an entrancepupil distance Z_(s) of the image sensor with respect to a minimum exitpupil distance L_(min) of the imaging optical system and the maximumexit pupil distance L_(max) of the imaging optical system satisfies acondition of$\frac{4L_{\min}L_{\max}}{L_{\min} + {3L_{\max}}} < Z_{S} < {\frac{4L_{\min}L_{\max}}{{3L_{\min}} + L_{\max}}.}$2. An image sensor in which a plurality of pixels each having aplurality of photoelectric conversion units for receiving light fluxesthat have passed through different partial pupil regions of an imagingoptical system are arrayed, wherein an entrance pupil distance Z_(s) ofthe image sensor with respect to a maximum image height R of the imagesensor satisfies the condition of2.33R<Z_(s)<6.99R.
 3. An image sensor in which a plurality of pixelseach having a plurality of photoelectric conversion units for receivinglight fluxes that have passed through different partial pupil regions ofan imaging optical system are arrayed, wherein a maximum image heightand an entrance pupil distance of the image sensor is determined suchthat a deviation amount between the entrance pupil of the image sensorand an exit pupil of the imaging optical system with respect to each ofthe plurality of photoelectric conversion units falls within apredetermined range.
 4. An image capturing apparatus that is capable ofconnecting to an exchangeable imaging optical system comprising theimage sensor as described in claim
 2. 5. An image capturing apparatusthat is capable of connecting to an exchangeable imaging optical systemcomprising the image sensor as described in claim
 3. 6. An imagecapturing apparatus comprising: the imaging optical system; and theimage sensor as described in claim
 2. 7. An image capturing apparatuscomprising: the imaging optical system; and the image sensor asdescribed in claim 3.